1. Technical Field
The present invention relates to the field of thin film write heads.
2. Background Art
Data is stored on magnetic media by writing on the magnetic media using a write head. Magnetic media can be formed in any number of ways, such as tape, floppy diskette, and hard disk. Writing involves storing a data bit by utilizing magnetic flux to set the magnetic moment of a particular area on the magnetic media. The state of the magnetic moment is later read, using a read head, to retrieve the stored information.
Data density is determined by the amount of data stored on an area of magnetic media and depends on how much area must be allocated to each bit. Data on magnetic media is often stored in a line or track. Magnetic media often have multiple tracks. In the case of the disk, the tracks are nested annular rings. More bits per ring and more rings per disk increases data density. Data density, therefore, is determined not only by the bit length, but also by the width of the bit which determines the track width. To decrease bit size, head size is decreased by fabricating thin film read and write heads with smaller track widths. Thin film heads commonly employ separate write and read heads.
Typically write heads do not contact the magnetic media but instead are separated from the magnetic media by a layer of air or air bearing. Magnetic flux generated between poles of the write head acts across the air bearing to change the magnetic moment of an area on the magnetic media.
Thin film write heads are typically formed by depositing and etching layers of magnetic, non-magnetic, dielectric, and electrically conductive materials to form the structures of the head, such as a core, a conductor winding, and upper and lower pole structures.
The rate or frequency that data is stored to the media is an important measure of the operational performance of the write head. One way to improve the operating frequency of the write head is to reduce the length of the pole structures, such as the yoke, to decrease the head inductance and the magnetic flux rise time. The operating frequency is determined, in part, by the structure of the write head and the materials used. The efficiency of the write head is also increased by reducing the yoke length.
Typical conductor windings of write heads are formed by first depositing a seed layer on a cured photoresist layer. To form the conductor winding, a photoresist pattern is formed on the seed layer by depositing photoresist on the seed layer, exposing to light through a photo mask, and removing a portion to form a trench extending to the seed layer. The trench defines the placement and dimensions of the conductor that forms the winding. The conductor winding typically is deposited by electroplating with copper to form the conductor winding within the trench on the exposed seed layer.
After forming the conductor winding, the photoresist pattern is stripped, and a wet chemistry etch is used to remove the remaining copper seed layer. As the seed layer typically is removed by wet chemistry etch, part of the winding conductor material is also etched away. The winding is surrounded with photoresist, which is cured to form an organic dielectric insulation.
Additional conductor windings typically are formed over the above described winding in a similar fashion, and electrically connected to it to form a multi-layered conductor winding.
One problem with the above process is that it limits the minimum dimension of the winding. The distance between corresponding edges of successive conductor turns, referred to as the pitch, and the height of the conductor are limited by photolithographic techniques. As such the height to width ratio or aspect ratio of the conductor is usually less than about 1.5. In addition, the minimum width of the photoresist defining the trench typically is greater than about 0.4 microns.
Another drawback of the above process and structure is that it produces a coil structure with a high overall stack height. Because the pitch is limited and the total length of the coil winding is relatively long, the conductors are often formed having greater height to provide sufficient cross sectional area in order to achieve sufficiently low coil resistance. In addition, a second or even a third winding layer often is formed to increase the number of coil turns without drastically increasing the yoke length to improve the operation of the winding. Also, because cured photoresist is difficult to form in extremely thin layers, the cured photoresist insulation typically formed under the conductor winding significantly increases the overall stack height.
High stack height makes it difficult to control the width of the upper or P2 pole tip in certain write head designs, thus leading to increased track width sigma. The increased stack height can cause problems with focusing and scattering during the exposure process, as well as problems of shadowing during pole trim process.
In addition, high stack height can cause reliability problems, such as cracking of the magnetic yoke material at the apex, or on the sloped surface between the top of the stack and the pole tip. Also, the steep slope associated with the high stack height causes the magnetic properties of the yoke material to degrade.
Furthermore, thermal stability is a problem with the structure described above. There is a large thermal expansion mismatch between the metal and the surrounding cured photoresist. The coefficient of expansion of the cured photoresist xcex1resist is greater than about several times the coefficient of expansion of the conductor xcex1metal. This can cause separation of yoke from the underlying insulation when the head is heated to higher temperature during manufacture, or operation.
The preferred embodiment of the present invention provides a write head having an interlaced conductor coil winding and method of fabrication.
The interlaced winding may have alternating turns of a first and a second coil. In the preferred embodiment, the side walls of successive coil turns are separated by an ultra thin insulation, preferably formed by a layer of inorganic insulation. In the preferred embodiment, the side wall insulation defines the distance between the successive turns of the interlaced coil.
In a preferred method, the interlaced winding is fabricated by forming the first coil having turns which are separated by a space. The second coil is formed so that its turns are disposed between the turns of the first coil.
In one method of fabrication, a conductive seed layer is deposited on a generally planar insulative surface, such as a write gap, a middle coat, or other insulation layer on or above the lower yoke.
A resist mask structure may be formed on the seed layer to define the layout of the coil. With this method, conductive material is deposited on exposed seed layer in a channel defined by the resist mask, thus forming the turns of the first coil. The underlying masked portion of the seed layer may be removed after resist mask removal to electrically isolate the turns of the first coil.
With the preferred method, the second coil is formed after deposition of an insulation material on the side walls of the first coil structure. It is preferred to form a layer of inorganic insulation conformal with the first coil. As such, the inorganic insulation lines the space between the turns of the first coil. The turns of the second coil may then be formed between the turns of the first coil, with the sidewall insulation material defining the distance between successive turns of the first and second coil.
One method to fabricate the turns of the second coil is to deposit a second seed layer on the conformal insulation layer and use a resist mask to define the turns of the second coil between the turns of the first coil. The resist mask may be removed, after formation of the second coil, and the portion of the seed layer underlying the resist mask removed to electrically isolate the turns of the second coil.
The turns of the second coil may be isolated by dry or wet etching techniques, or, by lapping away the portion of the seed layer overlying the turns of the first coil, such as by a chemical mechanical polish. As such, in some embodiments, the second coil is unplanarized, while in other embodiments the second coil is planarized. In some embodiments, it is acceptable to lap into a portion of the conformal insulation layer overlying the turns of the first coil. With other embodiments, it even is possible to lap into the top portion of the turns of the first coil during this procedure. An optional capping layer, or other insulation layer, may be formed over any exposed conductor material to insulate the winding from an upper pole structure or other overlying structure. As such, in the cross-sectional view of some of the embodiments, the turns of the first coil appear to project upward from the lower insulation layer, while the turns of the second coil appear to depend downward between the turns of the first coil from an overlying capping layer, with insulation material disposed between successive coil turns, similar in appearance to the carved teeth of a Halloween xe2x80x9cJack-O-Lanternxe2x80x9d pumpkin.
In another method of the present invention, the second turns may be formed without using a resist mask over the first coil. With such a method, planarization may be used to remove the conductive material overlying the first coil to electrically isolate the turns of the second coil. As discussed above, the planarization may lap into the insulation layer or the turns of the first coil to define the turns of the second coil.
Some embodiments of the write head of the present invention may have multiple layers of conductor winding. The additional layers may be formed using conventional methods and structure, or may have the interlaced coil structure of the present invention.
An advantage of the structure and method of fabrication of the preferred embodiments of the present invention is that they allow for ultra-compact coils. That is to say, the separation between the coils is significantly reduced. This allows for reduced upper and lower yoke lengths, thus lowering impedance through the yoke to improve the operating frequency of the write head.
Another advantage of the structure and method of fabrication of the preferred embodiments of the present invention is that, it allows for a reduced height winding, which reduces yoke length and allows for a low apex angle over which to deposit the upper yoke. This allows high moment materials, which do not perform well when deposited over steep slopes, to be used to form the yoke. The lower stack height and corresponding lower apex angle, therefore, increases the materials available for use when forming the upper pole structure. High moment materials with low impedance to magnetic flux improve the operating frequency of the write head, and allow structures to carry greater magnetic flux without saturating. As a result, the head can write with both higher data density and higher data rate.